diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index 516f406aea07..5e536343e846 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -89,6 +89,7 @@ import { TuiPluginRuntime } from "../../plugin"
 import { DialogGoUpsell } from "../../component/dialog-go-upsell"
 import { SessionRetry } from "@/session/retry"
 import { getRevertDiffFiles } from "../../util/revert-diff"
+import { getCurrentSessionWithChildren, getFirstDirectChildSession, getSiblingSessions } from "./navigation"
 
 addDefaultParsers(parsers.parsers)
 
@@ -127,12 +128,8 @@ export function Session() {
   const { theme } = useTheme()
   const promptRef = usePromptRef()
   const session = createMemo(() => sync.session.get(route.sessionID))
-  const children = createMemo(() => {
-    const parentID = session()?.parentID ?? session()?.id
-    return sync.data.session
-      .filter((x) => x.parentID === parentID || x.id === parentID)
-      .toSorted((a, b) => (a.id < b.id ? -1 : a.id > b.id ? 1 : 0))
-  })
+  const children = createMemo(() => getCurrentSessionWithChildren(sync.data.session, session()?.id))
+  const siblingSessions = createMemo(() => getSiblingSessions(sync.data.session, session()))
   const messages = createMemo(() => sync.data.message[route.sessionID] ?? [])
   const permissions = createMemo(() => {
     if (session()?.parentID) return []
@@ -354,7 +351,7 @@ export function Session() {
 
   function moveFirstChild() {
     if (children().length === 1) return
-    const next = children().find((x) => !!x.parentID)
+    const next = getFirstDirectChildSession(children(), session()?.id)
     if (next) {
       navigate({
         type: "session",
@@ -364,9 +361,9 @@ export function Session() {
   }
 
   function moveChild(direction: number) {
-    if (children().length === 1) return
+    if (siblingSessions().length <= 1) return
 
-    const sessions = children().filter((x) => !!x.parentID)
+    const sessions = siblingSessions()
     let next = sessions.findIndex((x) => x.id === session()?.id) - direction
 
     if (next >= sessions.length) next = 0
diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/navigation.ts b/packages/opencode/src/cli/cmd/tui/routes/session/navigation.ts
new file mode 100644
index 000000000000..7402b00abb52
--- /dev/null
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/navigation.ts
@@ -0,0 +1,37 @@
+type SessionNavigationItem = {
+  id: string
+  parentID?: string
+}
+
+function sortByID<T extends SessionNavigationItem>(a: T, b: T) {
+  return a.id < b.id ? -1 : a.id > b.id ? 1 : 0
+}
+
+export function getCurrentSessionWithChildren<T extends SessionNavigationItem>(
+  sessions: readonly T[],
+  currentSessionID: string | undefined,
+) {
+  if (!currentSessionID) return []
+
+  return sessions
+    .filter((session) => session.id === currentSessionID || session.parentID === currentSessionID)
+    .toSorted(sortByID)
+}
+
+export function getFirstDirectChildSession<T extends SessionNavigationItem>(
+  sessions: readonly T[],
+  currentSessionID: string | undefined,
+) {
+  if (!currentSessionID) return undefined
+
+  return sessions.filter((session) => session.parentID === currentSessionID).toSorted(sortByID)[0]
+}
+
+export function getSiblingSessions<T extends SessionNavigationItem>(
+  sessions: readonly T[],
+  currentSession: T | undefined,
+) {
+  if (!currentSession?.parentID) return []
+
+  return sessions.filter((session) => session.parentID === currentSession.parentID).toSorted(sortByID)
+}
diff --git a/packages/opencode/test/cli/tui/session-navigation.test.ts b/packages/opencode/test/cli/tui/session-navigation.test.ts
new file mode 100644
index 000000000000..6ec3b69d546a
--- /dev/null
+++ b/packages/opencode/test/cli/tui/session-navigation.test.ts
@@ -0,0 +1,103 @@
+import { describe, expect, test } from "bun:test"
+import {
+  getCurrentSessionWithChildren,
+  getFirstDirectChildSession,
+  getSiblingSessions,
+} from "../../../src/cli/cmd/tui/routes/session/navigation"
+
+describe("getCurrentSessionWithChildren", () => {
+  test("returns the root session and its direct children", () => {
+    const sessions = [
+      { id: "root" },
+      { id: "child-b", parentID: "root" },
+      { id: "grandchild", parentID: "child-a" },
+      { id: "child-a", parentID: "root" },
+    ]
+
+    expect(getCurrentSessionWithChildren(sessions, "root")).toEqual([
+      { id: "child-a", parentID: "root" },
+      { id: "child-b", parentID: "root" },
+      { id: "root" },
+    ])
+  })
+
+  test("returns the current child session and its direct children", () => {
+    const sessions = [
+      { id: "root" },
+      { id: "child-a", parentID: "root" },
+      { id: "child-b", parentID: "root" },
+      { id: "grandchild-b", parentID: "child-a" },
+      { id: "grandchild-a", parentID: "child-a" },
+    ]
+
+    expect(getCurrentSessionWithChildren(sessions, "child-a")).toEqual([
+      { id: "child-a", parentID: "root" },
+      { id: "grandchild-a", parentID: "child-a" },
+      { id: "grandchild-b", parentID: "child-a" },
+    ])
+  })
+
+  test("returns an empty list when the current session is missing", () => {
+    expect(getCurrentSessionWithChildren([{ id: "root" }], undefined)).toEqual([])
+  })
+})
+
+describe("getFirstDirectChildSession", () => {
+  test("preserves first-level descent from the root session", () => {
+    const sessions = [
+      { id: "root" },
+      { id: "child-b", parentID: "root" },
+      { id: "child-a", parentID: "root" },
+    ]
+
+    const visibleSessions = getCurrentSessionWithChildren(sessions, "root")
+
+    expect(getFirstDirectChildSession(visibleSessions, "root")).toEqual({
+      id: "child-a",
+      parentID: "root",
+    })
+  })
+
+  test("nested descent skips the current child session and selects its direct child", () => {
+    const sessions = [
+      { id: "root" },
+      { id: "child-a", parentID: "root" },
+      { id: "child-b", parentID: "root" },
+      { id: "grandchild-b", parentID: "child-a" },
+      { id: "grandchild-a", parentID: "child-a" },
+    ]
+
+    const visibleSessions = getCurrentSessionWithChildren(sessions, "child-a")
+
+    expect(getFirstDirectChildSession(visibleSessions, "child-a")).toEqual({
+      id: "grandchild-a",
+      parentID: "child-a",
+    })
+  })
+
+  test("returns nothing when there are no direct children", () => {
+    const visibleSessions = getCurrentSessionWithChildren([{ id: "root" }], "root")
+
+    expect(getFirstDirectChildSession(visibleSessions, "root")).toBeUndefined()
+  })
+})
+
+describe("getSiblingSessions", () => {
+  test("keeps sibling cycling scoped to the current depth", () => {
+    const sessions = [
+      { id: "root" },
+      { id: "child-b", parentID: "root" },
+      { id: "child-a", parentID: "root" },
+      { id: "grandchild-a", parentID: "child-a" },
+    ]
+
+    expect(getSiblingSessions(sessions, { id: "child-a", parentID: "root" })).toEqual([
+      { id: "child-a", parentID: "root" },
+      { id: "child-b", parentID: "root" },
+    ])
+  })
+
+  test("returns an empty list for the root session", () => {
+    expect(getSiblingSessions([{ id: "root" }], { id: "root" })).toEqual([])
+  })
+})